The genetic differences in 32 populations ofHydropsychebelonging to nine species distributed in Sicily, and central and southern Italy were assayed by horizontal starch gel electrophoresis. Larval specimens were examined. Twelve enzyme loci were assayed and allele frequencies, variability parameters, and Nei's genetic distance were calculated. The percentage of polymorphic loci ranged from 8.3 to 50.0%, the mean number of alleles per locus from 1.1 to 1.8, and the mean observed heterozygosity from 0.009 to 0.123. Nei's genetic distances values between conspecific populations ranged from 0 to 0.096; in the comparison between populations from Sicily and Calabria,H. doehlerihad the highest values. Only forH. spiritoithere were differences among the Sicilian populations. From genetic distance data, a dendrogram was obtained. At interspecific level, the values of genetic distance between conspecific populations ranged from 0.201{H. spiritoi ‐ H. gereckei)to 1.135(H. dinarica ‐ H. klefbecki). Genetic data were in agreement with morphological data.